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DI-85

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Power Integrations

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Power Integrations reserves the right to make changes to its products at any time to improve reliability or manufacturability. Power Integrations does

not assume any liability arising from the use of any device or circuit described herein. POWER INTEGRATIONS MAKES NO WARRANTY HEREIN AND

SPECIFICALLY DISCLAIMS ALL WARRANTIES INCLUDING, WITHOUT LIMITATION, THE IMPLIED WARRANTIES OF MERCHANTABILITY, FITNESS FOR A

PARTICULAR PURPOSE, AND NON-INFRINGEMENT OF THIRD PARTY RIGHTS. The products and applications illustrated herein (transformer construction and

circuits external to the products) may be covered by one or more U.S. and foreign patents or potentially by pending U.S. and foreign patent applications assigned to

Power Integrations. A complete list of Power Integrations' patents may be found at

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under certain patent rights as set forth at http://www.powerint.com/ip.htm.

The PI logo, TOPSwitch, TinySwitch, LinkSwitch, DPA-Switch, EcoSmart, Clampless, E-Shield, Filterfuse,

PI Expert and PI FACTS are trademarks of Power Integrations, Inc. Other trademarks are property of their respective companies.

©Copyright 2005, Power Integrations, Inc.

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Figure 3. No-load Input Power vs. Line Voltage.

Figure 4. Efficiency vs. Output Power and Line Voltage.

Figure 2. Output VI Characteristic Curves vs. Load & Line

Key Design Points

• The PI Xls spreadsheet calculates all of the parameters

required to specify and build transformer T1.

• This design uses one of two “standard” transformers (see

AN-39). With this transformer, the output voltage of the

supply can be set between 4 V and 7.5 V by selecting the

appropriate value of R1.

• Figure 1 contains three optional components: RF1,

VR1 and C4. A fusible resistor must be used if a safety

agency disapproves of using L1 as a fusible component.

The auto-restart function limits the output power

during open loop operation, so only a 1/2 W VR1 is

required if the open loop output voltage is unacceptable.

Y capacitor C4 improves EMI repeatability but is not

required to meet EMI limits.

• FortheICtolimitthesupplyʼsoutputcurrentpastthepoint

of peak power delivery, the voltage on the FB pin must

begintodropbelow1.69Vastheloadincreases. Therefore,

the value of R1 should be selected so the FB pin voltage is

1.69 V at the peak power point.

0

0.2

0.1

0.4

0.5

0.3

0.6

0.8

0.9

0.7

1

Average Output Current (A)

10

9

8

7

6

5

4

3

2

1

0

90 VDC

115 VDC

230 VDC

265 VDC

Min Limit

Max Limit

50

100

150

200

250

300

AC Input Voltage (VAC)

160

140

100

120

60

80

40

20

0

0.00

0.50

1.00

1.50

2.50

2.00

3.00

Output Power (W)

80

70

50

60

30

40

20

10

0

90 VDC

115 VDC

230 VDC

265 VDC